Beyond the Bloom: What Really Attracts Bees to Gardens (Ep. 64)

Urban park or cattle field? Bees don’t care where your garden grows. What do they care about? The right flowers, in the right place, at the right time. Our guest, Dr. Laura Russo, discusses her study on how different types of gardens and surrounding landscapes affect bee populations. Her team planted identical research gardens across vastly different landscapes—from urban parks to cattle-grazed fields—and found that pollinator diversity and abundance remained surprisingly consistent. Even gardens surrounded by flower-rich botanical settings didn’t outperform those in barren agricultural zones.

So what does matter? Laura says it’s all about the quality and visibility of the flowers themselves. Bees are picky eaters with strong preferences for specific host plants—and they’re willing to travel farther than we thought to find them. Ornamental blooms might dazzle the human eye, but they often leave pollinators hungry.

Dr. Laura Russo is an Assistant Professor in the Department of Ecology and Evolutionary Biology at the Universty of Tennesse, Knoxville. Her research team for the study we discussed included Devon S. Eldridge, Amani Khalil, and John K. Moulton. The Russo Lab looks at the structure, management, and function of mutualistic interactions in a variety of systems, especially focusing on the biodiversity and conservation of plant-pollinator interactions.

Good to know

Laura mentioned that in their study they counted the number of inflorescences of each plant species. An inflorescence is the complete flower head of a plant including stems, stalks, bracts, and flowers. A bract is a modified leaf with a flower or cluster of flowers in its axil. Think of a poinsettia plant – the colorful “flowers” of poinsettias are actually bracts.

Transcript

Jacy: [00:00:00] Welcome to the Bees Knees, a podcast wild about native bees. Wild and native bees are under threat worldwide. In each episode, we look at actionable things we can do to support these adorable little guys whose pollination work is crucial for maintaining biodiversity. I’m Jacy Meyer, and I thank you for being here.

Plant lots of flowers, save the bees. I’m gonna seem a bit contrarian today. We talk a lot about the importance of making sure there are a variety of flowers to support bees, but today’s episode put some nuance into the conversation. Dr. Laura Russo and her students conducted a seemingly straightforward study exploring how different types of gardens and the surrounding landscape affect bee populations in eastern Tennessee.

What they found surprised, even them, so your research found that just having [00:01:00] a diverse mix of flowers nearby doesn’t necessarily mean more bees will show up. Can you explain why local floral diversity isn’t always enough?

Laura: Yes. So this was an interesting and unexpected finding of this study and to explain a little bit more about the background of the study and how we asked these questions.

Um, these were controlled experimental research gardens. And this is extremely important point because each of the gardens had exactly the same composition of species, number of species, and number of individuals, and those were replicated at the landscape scale. So previous research had shown that land use at a broad scale does influence pollinator communities.

Both in terms of composition of the species that are there, the diversity and the abundance of pollinators, but those studies were observational. They were not controlling the plants that they were surveying. In our study, we did control the [00:02:00] plants, and we expected that in landscapes where there were fewer resources overall around those gardens, we would see that effect in the garden, that there would be fewer pollinators in the garden.

But instead, what we found was if you’re controlling for the gardens themselves, the land use doesn’t really have that much of an impact, at least not as much as you’d think. There were some insects that did respond to that land use. One of those was honeybees. Honeybees were more abundant in urban landscapes.

There’s also soldier beetles, which were more abundant in agricultural landscapes. But if you look across the whole pollinator community. And you’re interested in diversity or abundance in general? Really the land use didn’t have a big effect, and this is especially striking when we’re taking, you know, some of these research sites that were in agricultural landscapes, like cattle forage, where around these research gardens, there was [00:03:00] nothing just, you know, grass that had been grazed down to the ground basically.

And we were comparing those to gardens. The same research gardens placed in a botanical garden that was blooming year round with just a huge diversity and abundance of flowers. And yet those gardens had the same abundance, composition and diversity of pollinators. So that was a very unexpected finding.

Jacy: And do you have any thoughts about why that could be?

Laura: So I think what this means is two main findings from my perspective. One is that bees in particular, they really care about their host plant. So a lot of these are strongly tied to their favorite plant that they feed on. It’s like their favorite food resource.

And they’re gonna find that plant, and if you have it, they’re gonna visit it probably. Um, the second thing I think it means is that they [00:04:00] can probably travel a lot farther than you think they can. These insects are used to a highly dynamic and variable resource landscape. If you think about just the area around you, what’s in bloom at any given time and where that’s located is extremely variable.

So they’re very good at finding resources. At a landscape scale, and you know, a lot of research will suggest that small bees can only travel like a hundred meters from their food, from their nest, but I think this suggests that they could actually travel a lot farther to find their food resources. And that makes sense.

’cause if bees could only travel a hundred meters, how would they deal with this extremely changeable landscape of resources? Right. So in my opinion that those two things are, are takeaway messages from the study.

Jacy: That’s very, very interesting. So, because we do find gardens or [00:05:00] areas that seem to be bee magnets, while other areas don’t get Yes.

The visitation that we might wanna see. Based on what you’ve learned, what would you say are the most important things people could do to make their gardens more inviting to pollinators?

Laura: Well, one thing we’ve found over the years, and not necessarily in this study specifically, but you know now I’m drawing from all of my labs, research is the quality of those floral resources is it really matters, and they’re very particular about that.

And ornamental plants have been selected for their attractiveness to humans and not their attractiveness to insects. So when you see a group of plants and they’re literally buzzing with insects, those tend to be flowers that are very accessible and they have a lot of floral resources. And that makes them very attractive to a wide range of insects.

And you know, a [00:06:00] garden that is aesthetically beautiful to a human that has lots of large blossoms, but maybe they’re ornamental, it’ll be a lot quieter because it’s not necessarily providing the floral resources in terms of pollen and nectar. That those insects are looking for. So it’s not necessarily just, oh, I have a lot of flowers.

They’re particular about what flower that is and what it is offering, if that makes sense.

Jacy: One of the things you mentioned was that floral display size seem to be a key factor. Could you define that? What does that mean exactly?

Laura: So in this study we count the number of inflorescences of each plant species that is open on a given sample date.

So we have coupled the number of open inflorescences with the number of visitors we get. And then in addition to that, we also measure the size of these inflorescences . So we have now calculated what we call [00:07:00] floral area, the number times the average surface area of the floral. Display. Um, and we’re calling that display because it’s not necessarily the amount of pollen or nectar that’s available, it’s just how showy is this plant species on the day when we were collecting insects on it.

And then we can couple those things, the size of the display and the number of insects that visit, and we can see that basically the showier, the flowers are in general, the more insects they have. Which probably is a proxy for the amount of resources they have or maybe just how apparent they are at the landscape level.

Jacy: So talking about the different landscapes, you studied these gardens in different landscapes, so cities, forest farms, and you kind of touched on this a bit at the beginning, but did anything else unexpected stand out about how bees respond to these settings? And I’m kind of especially thinking about in urban areas.

Laura: Yes, [00:08:00] the results we got were not at all what I expected, just to be honest with you. Um, based on previous research and seeing the kinds of landscapes that had the highest bee, diversity and abundance, I was expecting that our more forested landscape, which was at the arboretum, I thought that would have the highest abundance in diversity.

But that didn’t actually seem to matter when we controlled for these plants and the urban sites, you know, those were sites where it’s not just about the amount of impermeable surface, which is what we call, you know, pavement or nothing can grow. It’s not just about that for these urban areas, because they are being actively managed to have flowers year round.

So those urban sites are interesting in the sense that it’s not necessarily like at the landscape level, you would think that those resources would be lower quality, but then there’s so many flowers year round that at least there’s something there. [00:09:00] And then that’s interfacing with the fact that most of those points are ornamentals and might not actually have any resources.

So those interactions are kind of complicated. But you know, just standing on the ground and looking at those different sites, you would assume. That the cattle forage site where you can just look around and see in all directions, there’s nothing blooming. You would just assume that that would have fewer pollinators and yeah, it wasn’t significantly different.

So that was very surprising. But yeah, in terms of like what I expected going into this study, it was not what we found in the end. So I had to revise my assumptions once we saw the data. This is just another angle. So Manny, my student was interested in land use and how that influenced pollinator communities.

But Devin, who was the lead author, I think on the paper that you’re referring to, she was interested in whether or not these agricultural systems lead to the homogenization of these [00:10:00] pollinator communities. So this is a slightly more complicated concept, but the idea is that in anthropogenic or human modified landscapes.

We expect these communities to become more and more similar because we’re probably losing specialists from those landscapes. And so her effort was, she was serving the area around the research gardens and then comparing pollinators in that area to the pollinators in the gardens with the hypothesis that agricultural landscapes, those two things would become more and more similar.

And we also did not find support for that. So that could just be an artifact of how specialized these insects are on their host plants, that basically they’re very consistently visiting the same plants no matter what’s in their area. And so it might not necessarily mean that agriculture doesn’t have that impact.

But that bees are not necessarily the group of organisms that are gonna reflect that pattern. If [00:11:00] you’re providing their host plants, then they’re gonna show up. And then the other key element that I should note is this study was conducted in eastern Tennessee, which is. Overall, not a super heavily modified landscape relative to other types.

So like the highest proportion of agriculture we had in the landscape was about 70%, which is a lot, but it means that there are still patches of habitat. And I’m putting that in there because one could assume that if you reach even higher levels of landscape modification that this pattern might vanish.

Like there’s probably some threshold at which if you passed it, you would not get bees. But our landscapes were diverse enough and patchy enough with resources that we didn’t see that. So that’s just a caveat about how the extent of land use modification could be playing a role here that wasn’t captured in our study.[00:12:00]

Jacy: What are you thinking about going forward?

Laura: Research wise, I have two main areas that I think would be really important moving forward. I’m still very focused on nutrition for these pollinators. Just like us, pollinators need a diverse diet with lots of protein and fat, and so they care a lot about the nutritional quality of their resources.

They’re very sensitive to even subtle changes in that nutritional quality and that nutritional quality in the plants is affected by what chemicals the plants are exposed to, what their stress level is. Are they experiencing drought or heat waves? Their resource quality is changing under all those conditions, and they’re not all equal in what they offer in terms of how much, how accessible, and what quality it is, so I’m fascinated by that interface.

And in terms of conservation or planting for pollinators, considering what the best nutrition for those pollinators is, I think [00:13:00] is critical. We can’t just like throw things out there without considering what they’re providing. So that’s one angle with the research. The second angle that is maybe harder to directly address is.

How dynamic at the landscape level, the phenology or the timing of flowering of these different plant resources is over space. Just space and time and how these insects are able to respond and adapt to those really changeable landscapes. And just as you know, a personal anecdote, someone who’s been studying this a couple years ago, I was looking for a very specific bee species.

And it was a very common bee species that’s very generalist. It’ll visit anything basically. But I needed live specimens for a collaborator to look at their immune response in real time. So I had to collect them within an hour of this assay that was gonna be conducted, and they all had to be alive. And that meant that I had to go out that day and find where the [00:14:00] bee was on that day, and I have my bicycle, and I was cycling around Knoxville looking for patches of flowers on which I could find this bee.

And I learned very quickly that that patch of flowers is not gonna be there the next week. It’s gonna be somewhere else entirely in town. So I’m cycling tens of miles trying to find patches of flowers at the landscape level, thinking these are the same bees that are finding these flowers every week, and they can find them better than I can, so, so there’s something about that that is really interesting.

Thinking about how opportunistic these insects are and how good they are at adapting to really changeable conditions is something I’m very interested in.

Jacy: So my last question, and you kind of touched on this a little bit, if you could encourage people to do just one thing to support Native bees, what would it be?

Laura: Well, the great thing about pollinator conservation is that we can all do something because [00:15:00] the more flowers, the better. But if you wanna like step it up a level, then thinking about the kinds of nutrition you’re providing and the kinds of resources you’re providing, I think is another level. And you could even think about that at a year long scale.

So you want something flowering at all times of year. And if you are really interested in native and wild bees, then you should start thinking about their host associations. So you can get these really specialist bees by planting their favorite host plant. And there are lots of examples of this, but for example, iron weed is blooming right now.

It’s a lovely purple flower, and there’s a bee that specializes on it, and Melissodes denticulatus that has blue eyes and I call them my blue eyed bees. They’re beautiful. If you plant iron weed, you will get these bees. They love that plant, they will find it. Uh, and there are so many examples of [00:16:00] that. You know, there’s a bee that specializes on ground cherries, so if you plant ground cherries you’ll have halictoides and so on and so on.

And so I think if you’re someone who gets excited about diversity and specialization, then bees are a fun group to work with. ’cause you can like find your specialist Bee by planting its host plant. Very easily

Jacy: fascinating, wasn’t it? I love how Laura was so open to the ideas that her students brought and that together they learned something not only interesting, but extremely beneficial.

Although the size and diversity of local floral resources might not significantly impact be abundance, the diversity of plants and the floral display size in garden plots can make a difference. A huge thank you to Laura for the great conversation and to you, my great listener for spending some time with me.

Thank you for sharing the bees knees with friends and family. Your support means a lot. Until next time, stay [00:17:00] curious.